The present invention relates to a radial piston pump for a hydraulic anti-lock brake system. At least one pair of pistons are provided which alternately perform working strokes and are arranged in a stationary cylinder block with working chambers comprising inlet valves and outlet valves. An eccentric shaft controls the radial movement of the pistons and an annular device interconnects the end portions of the pistons.
In a known radial piston pump of this type (German published patent specification No. 16 53 637 which corresponds to U.S. Pat. No. 3,514,224), the eccentric shaft is slidably supported in an axial bore of the cylinder block. This necessitates that the surface of the cylinder block bore and of the eccentric shaft are precisely machined. Nevertheless, these surfaces are subjected to considerable wear. The pistons with their radially inner ends slide on eccentric bushings encompassing the eccentric. The consequence of this is wear due to friction on the pistons and the eccentric bushings.
The annular device connecting the end portions of the pistons consists of a one-part coupling ring which engages with axial extensions into annular grooves of the radially outer end portions of the pistons and which ensures that the pistons are forced to return from the upper to the lower dead center. Hence, unlike in other known radial piston machines, this return is not dependent on the centrifugal force, and delivery is possible until the lowest number of revolutions. Thus, the coupling ring merely causes resetting. However, it is placed in an axially open annular groove of the cylinder block and is axially secured in position therein by an axial cylindrical projection of the pump housing. Hence, its diameter is comparatively large, and it is in abutment on the cylinder block and the pump housing on both sides thereof, it is exposed to large-surface frictional stress.